Alkali metal salts of citric acid (particularly tri-sodium citrate) are useful in various products and processes such as ion exchange resin regeneration, cement retardation and electro as well as electroless plating.
Tri-sodium citrate dihydrate is also useful as a detergent builder and is a viable alternative to tripolyphosphate, the work horse of detergent builders, because it is nontoxic and readily biodegradable. However, the relatively high cost of this material has limited its acceptance by the detergent industry.
In the United States, citric acid is primarily produced by fungal fermentation of carbohydrates using selected strains of Aspergillus niger. This process results in the formation of citric acid-containing liquors which are impure materials containing sugars, salts, biomass, and up to about 85% by weight citric acid. Extensive purification is required to provide a citric acid product which is suitable for food and pharmaceutical specifications. These purification techniques increase the cost of the product while also providing a material which is of greater purity than that which is required for use as a detergent builder.
Shen, in JAOCS, Vol. 61, No. 6 (June 1984), describes a process for the recovery of an impure tri-sodium citrate which involves adding methanol to a hot solution of citric acid which has been converted to tri-sodium citrate by the addition of sodium hydroxide thereto to cause precipitation. The present invention was reduced to practice in the United States before the publication date of this article.